1. Technical Field of the Invention
This invention relates to exercise machines, and more particularly, to resistance members for resisting movement of components on a multipurpose exercise machine.
2. Background Art
Exercise apparatus exist in many configurations. Typically each configuration is intended to exercise certain muscle groups of the body by moving a member of the body in a specific way or through a selected range of motions, usually intended to represent an athletic activity or otherwise physiologically beneficial motion. The member of the body typically works against a resistance as it moves through the desired motion.
Dead weights, also called free weights, such as dumbbells and barbells, have been used for progressive resistance exercises. More recently, other forms of resistance equipment have used friction pads, springs, flexible bands or hydraulic cylinders. These forms of resistance can be cumbersome to use and may not represent a preferred resistance through an entire range of motions or for different exercises using the same resistance.
It is presently believed that a substantial resistance is desirable at initial deflection, i.e., the start of an exercising motion by a user. An increase of resistance during the exercising motion is also desirable. It is further believed that a nearly ideal resistance plot or curve (of resistance verses deflections) would be biased upward to have a pre-selected non-zero value immediately upon deflection by a user, followed by a tailored linear increase in resistance up to maximum deflection.
Thus, it is desirable to have a resistance device that can be pre-loaded to provide resistance immediately upon deflection by a user. It is also desirable that the force curve of such a device be curved upward in proportion to the amount of preloaded resistance. Optimum resistance force over the entire range of motion is then available.
Prior art devices, such as springs and hydraulic cylinders, do not meet this need. For instance, a conventional spring mechanism may not provide a high level of initial resistance and may not display linear resistance through the full range of travel. In addition, a spring having a high spring constant may result in an unacceptable high level of maximum resistance. Hydraulic shock systems fail to meet the needs described above because they typically cannot be preloaded and do not provide an increase in resistance throughout the range of motion or deflection. Further, the heating of the fluid with repetitions can affect resistance.
If one were to select an elastomeric resistance, it may break more readily than other resistance devices and also become entangled in the equipment. One proposed method for dealing with breakage is to include a mechanism to retain or contain the elastomeric elements. However, such a capture mechanism must be moved whenever the elastomeric element is moved to adjust the level of resistance. In addition, the elastomeric element cannot be removed for adjusting resistance if it is pre-loaded.
Consequently, there is a need for a resistance device that can be easily biased at initial deflection and is conveniently adjustable by the user without requiring the user to leave the machine or change position. In addition, such a device would be properly restrained should breakage occur.